In the field of construction of buildings and the like, a vibrator or vibrators are used for providing certain vibrations into wet concrete, cement and the like. In this case, the vibration speed (v.p.m.) of the vibrator is selected according to the kinds of the cement or slab structures. For example, vibration speeds of 1,500 v.p.m., and 9,000 v.p.m., are provided for rough particle structures and finely divided particle made structures, respectively. Provision of such vibration causes air gaps in the interior of the concrete, cement and the like to be eliminated and causes an increase of strength of the concrete. A fine aesthetic finish is achieved.
Conventional, known vibrators for such use employ a weight of a given weight on a rotary shaft of a motor and the motor is arranged to be rotated in a given direction, such vibrators have a given vibration speed, centrifugal force and vibration bandwidth. When the vibration speed is intended to be changed because the particle sizes of the structure materials are different, different vibrators conventionally have been needed, and such a requirement has proven quite uneconomic.